Field of Invention
The present invention is directed toward improvements in mass timber building construction, and more particularly, the procurement, prefabrication and construction of multi-story mass timber buildings made from fire-protected laminated timber products, offering improved defense against the ravaging and destructive forces of fire.
Brief Description of the State of Knowledge in the Art
Over the past few decades, there has been a movement towards using engineering wood products (EWPs) based on young immature timber growth, for reasons of sustainability, and the fact that old mature timber is either not available or too expensive to meet current market demands in the wood-framed building industry. When using engineered wood products EWPs, it is possible to fabricate wood beams, panels and assemblies that can span great lengths and support great loads, while being manufactured from small, young and immature trees, such as Fir, Spruce and Pine.
Among the many different kinds of EWP innovations developed over the years, mass timber products have been receiving growing interest. This interest is due primarily on the capacity of certain mass timber products (e.g. cross-laminated timber or CLT) to replace structural steel and concrete and many applications, and allow architects to design and construct high-rise and multi-story buildings 1 from mass timber CLT, as illustrated in FIG. 1A.
As shown in FIG. 1B, conventional mass timber building products can be organized into two product categories comprising: (i) glued products, including glue laminated timber (GLT) 2, structural composite lumber (SCL) 3, and cross-laminated timber (CLT) 4; and (ii) non-glued products, including dowel laminated timber (DLT) 5, nail laminated timber (NLT) 6, cross nail laminated timber (CNLT) 7, and interlocking cross laminated timber (ICLT) 8.
For over 20 years, conventional CLT products have been widely used in Europe, and in recent years, CLT products have been gaining ground in North America. The reasons for this growing interest is that CLT technology enables architects to design and construct buildings having great height and the capacity to sustain great loads presented during Earthquakes and other natural disasters. The environmental and construction benefits of CLT make it a growth industry, with more manufacturing plants opening each year.
Cross-laminated timber (CLT) is a promising wood-based structural component and has potential to provide cost-effective building solutions for residential, commercial and institutional buildings as well as large industrial facilities. Market acceptance of CLT requires that it meets the applicable building code requirements. CLT elements are used in building systems in a similar manner to concrete slabs and solid wall elements, as well as those from heavy timber construction, by avoiding concealed spaces due to the use of massive timber elements, thus reducing the risk of fire spread beyond its point of origin. Moreover, CLT construction typically uses CLT panels for floor and load-bearing walls, which allow fire-rated compartmentalization, thus again reducing the risk of fire spread beyond its point of origin.
In general, each CLT panel is custom built to the designer's specification. CLT panel size is governed by the press which typically measures 15 m×3.5 m. Panel thickness depends on the intended load and span. The most CLT panels have common configurations of 3, 5 or 7 layers, with cumulative panel thicknesses between 60 mm and 250 mm. The cross lamination feature of CLT panels provides dimensional stability, strength and rigidity. This makes CLT a viable alternative to conventional wood-framing, concrete, masonry and steel in many applications. CLT panels can be used to construct an entire mass timber building, as both the lateral and vertical load resisting system, or for select elements such as the roof, floors or walls. The CLT panel as a structural panel element is also used as a superior industrial matting, bridging and retaining wall product that replaces heavy timbers, steel, and concrete.
Below are some reasons why CLT has the potential to redefine construction around the world:                CLT panels can be produced in large size (up to 15 m×3.5 m and beyond), and fit together quickly on site making building construction much faster and easier.        For both large and small buildings, CLT panels connect together as a complete engineered wood building solution.        Each CLT panel is custom-made to suit the structural needs of the project and required appearance.        CLT panels are manufactured using the latest CNC machining technology to ensure high precision and eliminate site waste.        CLT panels are safe to erect, weighing only 20% as much as concrete.        CLT panels are safe to inhabit, being strong and flexible under load.        CLT is sustainable, as wood stores carbon to help our planet environmentally.        CLT panel construction out-performs conventional wood-framed construction in air-tightness, thermal insulation, internal moisture management, acoustic insulation and fire resistance.        For many building types, CLT construction systems out-perform steel and concrete on a basis of cost.        Also, CLT can be manufactured to customized dimensions and in varying panel sizes, while panel length is typically limited by transportation restrictions.        
FIG. 2 is shows a 3D CAD-based model 9 of the conventional multi-story high-rise mass-timber building being constructed from cross-laminated-timber (CLT) building components, supported on a concrete foundation.
FIG. 2A shows a cross-laminated timber (CLT) panel 10 being assembled, for use in the mass timber building shown in FIG. 2, shown constructed of layers of Spruce, Fir or Pine boards glued together, to provide maximum strength and durability, wherein the direction of wood grain in each layer is laid orthogonal to the direction of the grain of neighboring wood layers.
FIG. 2B shows a CLT element or panel 11, wherein factory-based computer-controlled (CNC) machinery is used to trim the CLT panel to exact dimensions, cut openings for windows and other installations, and support fabrication of the finished CLT panel destined for installation in a particular location in a specific mass timber building design.
FIG. 3 shows the various stages of processing supported within a conventional factory for producing cross-laminated timber (CLT) construction components. In general, a conventional CLT panel factory 12 comprises many stages including: a controlled drying stage 12A for drying structural timber 12B to a humidity of 12% + or − 2% or less and then visual or machine strength grading of boards; a finger jointing stage 12C for producing finger-jointed laminations from graded boards or board sections; a lamination planing stage 12D for planing and dimensioning finger-jointed laminations; a stacking and adhesive stage 12E for applying adhesive to the planed laminations; a stacking, pressing and curing stage 12F for pressing and curing the finger-jointed laminations with adhesive into a cross-laminated timber (CLT) piece using a hydraulic or vacuum process; a CNC fabrication stage 12G for trimming the dimensions of the CLT element, including cutting widows, doorways and other apertures required by the design; and a packaging stage 12H for packaging the CLT elements 12I for shipping to a building destination.
FIG. 3A shows a conventional CLT production line supporting a hydraulic press 13 for pressing and curing cross-laminated laminations (i.e. boards) with applied adhesive coatings, under great pressure, to product CLT elements. FIG. 3B shows a conventional CLT panel production line including an overhead crane 14 for picking up product CLT panels and moving them to the CNC machining stage, where CLT panels are carefully dimensioned and apertures are formed using CNC sawing and drilling operations. FIG. 3C is a conventional overhead CNC bridge 15 that moves along a CLT production line over a mounted CLT panel 17, in which apertures are carefully dimensioned and formed using CNC sawing and drilling operations. FIG. 3D shows a conventional display screen 16 on a computer workstation, displaying a model of the CNC bridge system used to fabricate a specific CLT panel from a standard CLT element, for use in a specific mass timber building project.
FIG. 4A shows a conventional CLT factory, in which a CLT panel 17 has been fabricated for a prefabricated mass timber building project, and shown being moved to temporary storage for shipping to a mass timber building construction site. FIG. 4B shows a conventional CLT factory, in which a set of CLT panels 18 have been fabricated and stored before shipment to the construction site of the prefabricated mass timber building.
FIG. 5A shows a 3D model 19 a conventional high-rise mass timber building with its crane 19A moving a prefabricated CLT panel 21 into position during the construction phase of the high-rise mass timber building. FIG. 5B shows the conventional CLT panel 22 being lifted off the ground for placement on the high-rise mass timber building being constructed in the background. FIG. 5C shows the conventional CLT panel 21 being lowered into position on a mass timber building being constructed, using the crane 20 shown in FIG. 5A.
Conventional CLT Panel Technology Falls Significantly Short on Providing Fire Protection
Despite performing well in standard ASTM E119 structural fire performance tests, and offering great promise as a cost-effective building solution for residential, commercial and institutional buildings as well as large industrial facilities, conventional CLT panels and assemblies generally fall short on fire protection and safety and can only offer a Class-B fire-protection rating based on ASTM E84 test standards. Such low fire-protection ratings are because conventional raw CLT has high flame spread rate (FSR) and high smoke development (SD) characteristics when a CLT panel burns in the presence of fire, ultimately producing a thick layer of char 23A from pyrolysis, as illustrated in the massive solid-wood CLT panel sample 23 shown in FIG. 6A. This charring of a CLT panel 23 can slow down the fire and protect the inner core from heating, while keeping CLT panels structurally sound, so that CLT panels, having more layers of wood, will last longer in a fire. However, as all CLT buildings rely on its Class B char value, architects are forced to specify that every CLT column and CLT panel is made thick and wide enough in size, from built up layers of laminated timber, so that the CLT panels will support fire longer than steel beams and columns, much like a tree in a forest fire. This overdesign requirement with conventional CLT panels increases the cost of CLT construction.
Moreover, conventional raw CLT does not offer any defense against “flashover” during a building fire. A flashover is the near-simultaneous ignition of most of the directly exposed combustible material in an enclosed area. When certain organic materials are heated, they undergo thermal decomposition and release flammable gases. Flashover occurs when the majority of the exposed surfaces in a space are heated to their auto-ignition temperature and emit flammable gases. Flashover normally occurs at 500° C. (932° F.) or 590° C. (1,100° F.) for ordinary combustibles, and an incident heat flux at floor level of 20 kilowatts per square meter (2.5 hp/sq ft). Firemen know this fact about raw conventional CLT building materials, and therefore will not defend a burning mass timber CLC building unless they are attempting to save human lives because of the dangerous condition raw CLT building material presents.
Therefore, there is a great need in the art to raise the bar on the limited fire-protection that Class-B charring offers to CLT building materials, and provide true Class-A fire-protection for tenants, fireman, police, first responders, building owners and visitors, and raise the standards of safety for humans who live and work in affordable buildings constructed using sustainable renewable resources, such as cross-laminated timber (CLT), and other engineered timber products.
In effort to prevent fire destruction of mass timber buildings, it is essential to understand the nature of the fire cycle before understanding how flame retardants, inhibitors and extinguishers work to suppress and extinguish building fires.
In FIG. 6B, the fire cycle 24 is graphically illustrated as having four essential components: (i) an ignition source (e.g., heat, incandescent material, a small flame); (ii) fuel material (e.g., wood, wax, fuel, etc.); (iii) oxygen; and (iv) free radicals (H+, OH−, O−) 25 associated with the combustion process.
In general, the ignition source can be any energy source (e.g. heat, incandescent material, a small flame, a spark, etc.). The function of the ignition source is to start the material to burn and decompose (pyrolysis), releasing flammable gases. If solid materials in the ignition source do not break down into gases, they remain in a condensed phase. During this condensed phase, the material will slowly smolder and, often, self-extinguish, especially if the material beings to “char,” meaning that the material creates a carbonated barrier between the flame and the underlying material.
In the gas phase, flammable gases released from the burning and decomposing material are mixed with oxygen, which is supplied from the ambient air. In the combustion zone, or the burning phase, fuel, oxygen and free radicals (i.e. H+, OH−, O−) combine to create chemical reactions 25 that produce visible flames to appear. The fire then becomes self-sustaining because, as it continues to burn the material, more flammable gases are released, feeding the combustion process.
In general, flame retardants, or fire inhabitants, act in three ways to stop the burning process, and consequently, can be classified by how these agents work to stop a burning flame. These three methods of flame retardation/inhibition/extinguishing are described below:
(i) Disrupting the combustion stage of a fire cycle, including avoiding or delaying “flashover,” or the burst of flames that engulfs a room and makes it much more difficult to escape;
(ii) Limiting the process of decomposition by physically insulating the available fuel sources from the material source with a fire-resisting “char” layer; and
(iii) Diluting the flammable gases and oxygen concentrations in the flame formation zone by emitting water, nitrogen or other inert gases.
One effective family of prior art clean fire inhibiting chemical (CFIC) liquid has been supplied by PT. Hartindo Chemicatamata Industri of Jakarta, Indonesia (a/k/a Hartindo Anti Fire Chemicals) for many years now, and used by many around the world in diverse anti-fire applications. Current chemical formulations marketed by Hartindo under AF11, AF21 and AF31 product designations, disrupt the combustion stage of the fire cycle by combining with the free radicals (H+, OH−, O−) that are produced during combustion.
Most prior art intumescent coatings, whether applied as paint or coatings on engineered wood products (EWPs), work differently from Hartindo's fire-inhibiting (anti-fire) chemicals, in that prior art intumescent coatings form a char layer when heated, acting as an insulating layer to the substrate of fuel source, to prevent the fuel source from burning. Prior art Pyrotite® magnesium-based cementitious coatings, as used in LP's FlameBlock® fire-rated OSB sheathing (i.e. sheeting), FlameBlock® I-Joists, and other FlameBlock® EWPs, release water when exposed to the heat of a fire, and thereby dilute the flammable gases and oxygen concentrations in the flame formation zone.
Another problem plaguing the mass timber market is that mass timber buildings are also vulnerable to mold and insects such as termites.
While various prior art methods have been proposed for providing fire-protection to engineered wood products (EWPs), such proposals have been generally inadequate, and there still exists a great need in the art for new and improved ways of providing EWPs with higher levels of fire protection, in the health and safety interests of building tenants and fireman.
Further, there is a growing demand for higher performance, fire-rated CLT building products for use in mass timber buildings in the single-family, multi-family and light commercial construction markets.
Also, there is a great need for better ways of designing and constructing high-rise and multi-story mass timber buildings that demonstrate improved defense against fire destruction, while overcoming the shortcomings and drawbacks of prior art methods and apparatus.